Many researchers have designed corneal prostheses and hundreds have been implanted. Pellier de Quengsy is credited with first suggesting the insertion of a glass plate into the cornea in 1771. These various designs met with varying degrees of early success, some with initial enthusiasm, and generally by disillusionment as the long-term complications occurred. Barber J. C., International Ophthalmology Clinics, 28:103-09 (1988).
Early corneal prosthesis designs involved imbedding a flat disk of alloplastic material into the cornea with a hole anterior to the prosthesis. Spool-shaped optical lenses were then placed in the hole through the cornea and the prosthesis. Another early design was an optical core held by plates attached to the core and engaging the anterior and posterior surfaces of the cornea. The posterior plate was inserted through an opening formed in the cornea, with a trephine and a relaxing incision which was the source of considerable complications.
Later, a two-piece, collar-button prosthesis was designed in which either an anterior or posterior plate was placed on a mushroom shaped part of the prosthesis, after the posterior plate was inserted through the cornea. This design was technically difficult and required special tools. Dohlman assembled his prosthesis of this design in a donor cornea before operating. Dohlman C. H., American Journal of Ophthalmology, 77:694-700 (1974). Dohlman used methylchloride to bond the two prosthetic pieces together, and, in some cases, also glued the prosthesis to the cornea with cyanoacrylate. The donor assembly was then sewn into the cornea of the patient during surgery as a penetrating keratoplasty.
More recent corneal prosthesis designs have had an optical core member held by a skirt or flange. Cardona H., American Journal of Ophthalmology, 54:284-94 (1962); Choyce D. P., Ophthalmic Surgery, 8:117-26 (1977). Cordona initially attached the skirt to the optical core member, but later went to a two-piece, nut-and-bolt design to allow adjustment of the height of the core above the conjunctiva. Choyce also used the two-piece design for adjustment in an early optical core-skirt prosthesis, as well as to facilitate removal of retroprosthetic membranes over the posterior surface of the core. Choyce buried the skirt with a flush core until the skirt was integrated into the cornea, and then replaced the original core with the optical core in a separate procedure.
The radial relaxing incision used in implanting these early prostheses was believed to be one of the reasons for their failure. As a result, Cardona developed a design in which the skirt of the prosthesis was placed in a lamellar pocket with the optical core extending anteriorly and posteriorly through the skirt. To avoid the relaxing incision, the lamellar pocket was made by a perilimbal incision before the central cornea was opened with a trephine. Melting occurred around the optical core with this design causing leakage, infection and extrusion. The intralamellar skirt was fenestrated to allow diffusion of nutrients and to increase incorporation into the tissue. Stone W. Jr., American Journal of Ophthalmology, 39(2):185-96 (1955); Choyce D. P., Ophthalmic Surgery, 8:117-26 (1977).
With the optical core and skirt designs of corneal prostheses, many skirt materials have been studied, including glass, polymethylmethacrylate, silicone, Teflon, Dacron, siliconed Teflon, Silastic, fiberglass, nylon, cellulose and a ceramic of aluminum oxide. Cardona H., American Journal of Ophthalmology, 64:228-33 (1967); Polack F. M. et al, Ophthalmology, 87:693-98 (1980); Polack F. M., British Journal of Ophthalmology, 55:838-43 (1971); Polack F. M., Cornea, 2:185-96 (1983); Kozarsky A. M. et al, Ophthalmology, 94:904-11 (1987); Heimke G. et al, Cornea, 2:197-201 (1983). Silicone was too soft and was found to become cloudy after some time period, fiberglass caused heavy vascularization and extrusion, and nylon worked well for awhile but later extruded. Cellulose caused inflammation, ulceration, opacification and extrusion. The ceramic of aluminum oxide showed early promise but mechanical problems and later complications prevailed. Of these materials, Dacron and siliconed Teflon proved to be the best, out these presented complications because of enzymatic degradation. These designs typically utilized a clinical grade (intraocular grade) polymethylmethacrylate or silicone optical core member of 2 to 5 millimeters in diameter, with the skirt of one of the above named materials having an outer diameter typically of 5 to 8 millimeters and glued or mechanically attached to the optical core member.
In an effort to obtain better biocompatibility, Strampelli and Marchi used tooth and bone to form the skirt to hold the optical core member in place. Strampelli B. et al, Ann Ottalmol Clin Ocul, 96:1-57 (1970). Blencke and colleagues tried to improve on this design by replacing the tooth with a glass ceramic. Blencke B. A. et al, Ophthalmologica, 176:105-12 (1978). However, incorporation of the prosthesis material into the corneal tissue proved to be a necessity. Glass, polymethylmethacrylate, cellulose and other nonporous materials did not allow for invasion by the fibrous tissue or vessels. Fibrovascular invasion of implant material has been demonstrated with porous polytetrafluoroethylene carbon fibers (Proplast), porous meltblown polybutylene, large pore Dacron mesh, expanded polytetrafluoroethylene (Gore-Tex) and porous polyethylene (Plastipore). Barber J. C. et al, Investative Ophthalmology and Visual Science, 19:182-90 (1980); Girard L. J., Cornea, 2:207-24 (1983); Trinkaus-Randall V. et al, Fifteenth Cornea Research Conference, Boston, September 1987; Kaiser D., Thorac Cardiovascular Surgery, 33:239-43 (1985); Dreikorn K. et al, Urology Research, 7:19-21 (1979). Of these skirt materials, expanded polytetrafluoroethylene, porous polyethylene and porous polytetrafluoroethylene carbon fibers have provided for good tissue growth, but long term complications have caused the prosthesis designs with these skirt materials to be unsuccessful due to melting, leakage and extrusion. Also, the prosthesis was often first installed in a remote site in the patient, such as a cheek, to allow growth of tissue around the skirt so that when later transplanted into the cornea the prosthesis had an increased likelihood of long-term stability.
Another problem with corneal prostheses of these various designs was overgrowth of the conjunctiva across the anterior surface of the optical core member, or the retraction and melting of the conjunctival tissue around the optical core member. Cardona H., American Journal of Ophthalmology, 54:284-94 (1962); Choyce D. P., Ophthalmic Surgery, 8:117-26 (1977). Cordona and Choyce reported that this is a function of the height of the optical core above the anterior conjunctival surface, and used an adjustable optical core to vary the anterior protrusion of the core preventing overgrowth. However, the anterior protrusion created problems as movement of the upper eyelid caused mechanical movement of the prosthesis and disrupted the stability of the means holding the prosthesis in place. This mechanical movement in turn caused enzymatic degradation, leakage and extrusion.